Userform1.Show

Private Sub TextBox1_KeyPress( _
  ByVal KeyAscii As MSForms.ReturnInteger)
  
    If KeyAscii = vbKeyBack Then Exit Sub
    
    ' Можно так ограничить.
    If InStr( 1 , "1234567890", Chr(KeyAscii)) =  0  Then
        KeyAscii =  0 
    End If

    ' Или так.
    'If Not Chr(KeyAscii) Like "[0-9]*" Then
    '    KeyAscii = 0
    'End If
    
    ' Или так.
    'If KeyAscii < Asc("0") Or KeyAscii > Asc("9") Then
    '    KeyAscii = 0
    'End If
    
    ' Или так.
    'If Not fnIsCharNumeric(KeyAscii) Then
    '    KeyAscii = 0
    'End If
End Sub

Public Declare Function IsCharAlphaA Lib "user32" ( _
  ByVal cChar As Long) As Long
  
Public Declare Function IsCharAlphaNumericA Lib "user32" ( _
  ByVal cChar As Long) As Long

Public Function fnIsCharNumeric( _
  ByVal intChar As Integer) As Boolean

    fnIsCharNumeric = IsCharAlphaNumericA(intChar) _
      And Not IsCharAlphaA(intChar)
End Function